Due to heavy consumption of electrical energy, a wide range of electrical equipment has heat radiating problem to a certain extent, for example, common high-power light emitting diode (LED) streetlights. The p-n junction temperature of a LED generally is not allowed to exceed a limit of 85° C. When the p-n junction temperature of a LED exceeds 85° C., the life of the LED will correspondingly reduce 50% with every 5° C. increase in the p-n junction temperature and brightness of the LED streetlight will decay 50% per half year. Therefore, the streetlight heat radiating problem, i.e., how to transfer the heat generated by the p-n junction of a LED to environment, has become a key issue in extending life expectancy and delaying brightness attenuation of a LED streetlight.
In prior art, a commonly adopted LED streetlight heat radiating structure is a die-casting or extruded aluminum alloy heat radiator. As shown in FIG. 1, LED bulbs 1 are mounted on bulb holders 2; an aluminum-alloy heat radiating base plate 3 is connected with the bulb holders 2 of the LED bulbs 1 by die casting; heat radiating fins 4 are perpendicularly connected on the heat radiating base plate 3. Normally, the heat radiating fins 4 are set to be extending outwards. In the process of implementing heat radiating, relying on metal thermal conductivity, heat generated by the LED bulbs 1 is transmitted via the bulb holders 2, the heat radiating base plate 3 and the heat radiating fins 4, and finally spread to the air. However, the aluminum alloy heat radiating structure has following defects: thermal conductivity coefficient of aluminum alloy is 100 W/MK; temperature decreases quickly along the distance of heat transmission; although this kind of heat radiator can be prepared with large superficial area, due to big thermal resistance of inner thermal conductivity, the heat radiator has a very small actually effective heat radiating area, which results in poor heat radiating effect.
Another LED streetlight heat radiating structure in prior art adopts a loop wick (LHP) heat radiator. LHP is a typical linear heat conduction element. The heat radiating principle is shown in FIG. 2. Heat radiating working substance is filled into a heat radiating loop tube 100, contacts with the heat generating area of the electronic element at an evaporating end 110, absorbs heat, and is evaporated from liquid working substance into gaseous state. After that, the heat radiating working substance flows from the evaporating end 110 of the heat radiating loop tube 100 to the condensing end 130 under the action of the wick 120. During this process, the heat is transmitted to a bigger heat radiating surface and the heat radiating working substance is transformed from gaseous state back to liquid state and returns to the evaporating end 110. When a LHP heat radiator is used as the LED streetlight heat radiating structure, the heat radiating loop tube is commonly disposed outside a lamp cap and the evaporating end of the heat radiating loop tube is usually arranged at a heat source which is usually at the top of the lamp cap. However, this kind of LHP heat radiating means also has the following problem: the heat radiating loop tube has small contacting area with the heat radiating area and the contacting thermal resistance is large, as a result, a large effectively extended heat radiating area can not be acquired and the heat radiating effect is undesirable.